Vehicle mounted hydraulic powered post puller

ABSTRACT

A hydraulically operated post-pulling apparatus adapted to be mounted on a motor vehicle, comprising a support adapted to be mounted on a vehicle, a telescoping boom pivotally mounted at one end on the support and having hydraulic cylinder means provided for extending and retracting the boom and for raising and lowering the boom, hydraulic cylinder means carried at the remote end of the boom for pulling out posts comprising a platform adapted to be positioned on the ground, hydraulic cylinder means mounted thereon, the other end of the hydraulic means being pivotally mounted to the end of the boom, hand actuated valves for operating the hydraulic cylinder means, and means carried at the end of the boom adapted to engage and grip a pole or post to be extracted.

United States Patent 1 1 1 1 3,848,850 Bemis Nov. 19, 1974 VEHICLE MOUNTED HYDRAULIC 3.019.918 2/l962 Keener 214/75 H POWERED POST PULLER 75 I t 1 h B Primary Examiner-Othell M. Simpson 1 men or J0 n emls Kalamazoo Mich Attorney, Agent, or Firm-Gordon W. Hueschen [73] Assignee: Bemis & Sons, Inc., Kalamazoo,

57 ABSTRACT [22] Flled: 1974 A hydraulically operated post-pulling apparatus [21] Appl. No.2 447,143 adapted to be mounted on a motor vehicle, comprising a support adapted to be mounted on a vehicle, a 'f l Apphcatlon Dam telescoping boom pivotally mounted at one end on the [63] Contmuatlon-ln-part of Ser. No. 320,163, Feb. 2, Support and having hydraulic Cylinder means provided 1973 abandoned for extending and retracting the boom and for raising and lowering the boom, hydraulic cylinder means car- [52] US. Cl 254/30, 214/3, 22554513224, tied at the remote end of the boom for pulling out posts comprising a platform adapted to be positioned on the g hydraulic cylinder means mounted 1 o earc 3 thereon, the other end of the hydraulic means being 5 9-31 124 pivotally mounted to the end of the boom, hand actuv ated valves for operating the hydraulic cylinder [56] References C'ted means, and means carried at the end of the boom UNITED STATES PATENTS adapted to engage and grip a pole or post to be ex- 2,2'44,899 6/1941 Smith 254/29 R tracted. 2,645.453 7/1953 Nelson 254/29 R 2,983,482 5/1961 Cary 254/132 17 Clalms, 10 Drawmg Flgures w /Z/ 5/ o 23 I 3 1 N 9 4 2 35 O I o 32 O ./2 46 /s 57 5/ 35 l 53 v- /Z i 5'2 1 l o 9 7 L 1 /1I a 4/1 PATENTE HEY I 9 I974 SHEET 30F 4 VEHICLE MOUNTED HYDRAULIC POWERED POST PULLER BACKGROUND OF THE INVENTION This is a continuation-in-part of application Ser. No. 320,163, filed Jan. 2, I973, now abandoned.

The present invention relates to apparatus for pulling embedded articles such as posts or poles (these terms are used interchangeably hereinafter) out of the 1 ground, and more specifically refers to such apparatus designed to be mounted on a motor vehicle and which may be utilized to pull posts from the ground, such as those supporting road signs adjacent to roads.

Apparatus for pulling posts out of the ground are known in the art. Some such apparatus are so designed that they must be handcarried to the site where they are to be used. Other apparatus, although designed to be vehicle mounted, are not provided with sufficient positive extracting force to be used for large or deep posts. Still others which are motor vehicle-mounted have no radius of operation or, at best, are confined to operation within an extremely limited radius from the vehicle.

OBJECT S OF THE INVENTION It is an object of the present invention to provide an apparatus for pulling posts or poles out of the ground which is adapted to be mounted on a motor vehicle. A further object is to provide such an apparatus adapted to exert a strong pulling force without requiring mounting on a heavy vehicle. Another object is to provide such an apparatus which, although mounted on a vehicle, can be operated so as to apply little or no force against the vehicle itself. An additional object is to provide an apparatus which is hydraulic cylinder-operated and powered by an engine on the vehicle, and having hand-operated controls convenient to the operating site. Yet another object is to provide an apparatus which may be utilized to extract poles located a substantial distance from the supporting vehicle. Still another object is to provide an apparatus which may be readily constructed of standard readily-available components and materials. Yet another object of the present invention is to provide an apparatus which may be relatively simply and rapidly operated even by unskilled workmen.

According to the invention, a pole-pulling apparatus is provided comprising a base which may be readily mounted to the frame of a vehicle by means of brackets. A telescoping boom is pivotally mounted to the support in such manner that it may swing angularly about a vertical axis. Additionally, hydraulic means is provided for extending and retracting the telescoping boom members and for raising and lowering the boom angularly. A post-pulling hydraulic cylinder is mounted at one end to the remote end of the boom and is provided with a ground-engaging platform at the other end. A hook is affixed to the end of the boom and adapted to engage a conventional chain and pulling jaw assembly. Manually operated control valves are mounted on the boom for controlling the operation of the various hydraulic cylinders. Operating hydraulic fluid under pressure is provided by a hydraulic pump which may be operated by the vehicle engine.

BRIEF. DESCRIPTION OF THE DRAWINGS In the drawings,

FIG. 1 is a side elevational view of the post-pulling apparatus of the invention shown mounted in storage position on a motor vehicle.

FIG. 2 is a partial rear end elevational view of the apparatus.

FIG. 3 is a side elevational view of the apparatus in 0 operating position.

FIG. 4 is a top view of the tower support, and

FIG. 5 is a schematic view of the hydraulic system.

FIG. 6 is a side elevational view of another embodiment of the invention.

FIG. 7 is an end view of the apparatus taken at the line 7 7 of FIG 6.

FIG. 8 is a fragmentary elevational view of the end of the apparatus showing another embodiment.

FIG. 9 is a fragmentary elevational view of still another embodiment of the invention, and

FIG. 10 is a fragmentary elevational view of the end of the apparatus of a further embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, the post-pulling apparatus 10 of the invention is shown mounted on a motor vehicle 1 l. The apparatus comprises a tower support 12 mounted on the vehicle frame. Mounted on the support 12 by suitable means such as welding is a vertical tower or post 14. A telescoping boom 15 is pivotally connected to the base of the tower 14.

Referring more specifically to FIGS. 2-4, the tower support 12 (FIG. 2) is in the form of a steel channel having mounting brackets 13 (FIG. 4) of suitable size and position affixed thereto at one end and mounted to the vehicle 11 at the other. At the remote end of the support 12 a base plate rest 18 is affixed by such means as welding having apertures 19 and recesses 20 (FIG. 4) to permit the anchor pins 48 of the base plate 47 to extend therethrough in the rest or storage position. A pair of clevis rings 21 and 22 are mounted on the tower l4 and have clevises 23 and 24 mounted rotatably thereon and lubricated by Alemite or Zurk Lub fittings 25 and 26. Thrust washers 27 are provided on each side of the clevises.

The telescoping boom 15 comprises a lower boom member 31, a lower boom extension member 32, slidably mounted within the lower boom member 31, and an upper boom extension member 33 welded to the lower boom extension member 32. In the preferred form the boom members are rectangular in crosssection, although other suitable forms may be utilized if desired. A hook 34 is welded to the end of the upper boom extension member 33. Affixed to the lower boom member 31 by means such as welding are a lower boom clevis 35, an upper boom clevis 36, and a control plate assembly 37. A boom tang plate 38 is provided at the end of the lower boom member 31 and is engaged by the clevis 24 by means of clevis pin 39 retained by a cotter pin. Additionally welded to the end of the upper boom extension member 33 is a boom extension clevis 41 having a boom extension tang 42.

Operation of the post-pulling apparatus of the invention is accomplished by means of hydraulic power furnished by the motor vehicle on which the apparatus is mounted, in combination with a plurality of hydraulically operated cylinders. A hydraulic cylinder assembly 44 is connected between the lower boom clevis 35 and the tower clevis 23, which causes the boom to be raised and lowered. A second hydraulic cylinder assembly 45 is pivotally affixed at its ends to the upper boom clevis 36 and the boom extension clevis 41. The operation of this assembly causes the upper boom extension 33 to be extended or retracted. A pulling hydraulic cylinder assembly 46 is connected at one end to the boom extension tang 42 and at the other end has a base plate 47 pivotally mounted thereto. The base plate 47 is provided with four anchor pins 48.

As shown in FIG. 3, a post 51 is engaged by means of conventional pulling jaws 52, such as those disclosed in US. Pat. No. 3,048,368, operated by means of a chain 53 engaged by the hook 34.

Control of the hydraulic cylinders is provided by means of operating levers 54, 55, 56, and 57. FIG. is a schematic drawing showing the operation of the various valves and cylinders. Power for the hydraulic cylinders is supplied by a pump 58 driven by the vehicle transmission through a power take-off. The valves 54', 55, and 56' are operated by operating levers 54, 55, and 56, respectively. The valves are conventional three-position valves which extend, retract, or place the cylinders in neutral position. Valve 57' operated by lever 57 is a relief valve. When relief valve 57 is closed, cylinder 44 operates normally. When relief valve 57 is open, all pressure on cylinder 44 is relieved, permitting boom to be raised or lowered as it is caused to move by the operation of pulling cylinder assembly 46. Pump 58 furnishes fluid under pressure to the valves through a common input line 61. Exhausted fluid from valves 54', 55', and 56' is returned by a common exhaust line 60 to a reservoir 59. Exhausted fluid from valve 57 is returned by exhaust line 62 to line 60.

When cylinder assembly 46 is operating for pulling posts, relief valve 57' must be in the open position to permit cylinder assembly 44 to float so that boom 15 y can be raised by the action of cylinder assembly 46.

The apparatus is placed in operation by swinging boom 15'horizontally to the area near where the post is to be pulled out. Boom 15 is then lowered by operating valve 54 until base plate 47 is slightly above ground level. Valve 55' is then activated to extend boom 15 in order to position base plate 47 next to the post. Valve 54' is then activated to lower base plate 47 to the ground. Pulling jaws 52 are then attached to the post and chain 53 placed over hook 34. Pulling cylinder valve 57' is then placed in the open position to relieve the pressure on cylinder assembly 44 and allow it to float." Valve 56' is then placed in the extend position to cause pulling cylinder assembly 46 to extend to its full limit. Pulling cylinder assembly 46 is then lowered again and pulling jaws 52 reset on the post. These steps are repeated until the post is free of the ground.

Referring to FIGS. 6 and 7 a post-pulling apparatus 65 in a modified embodiment is shown comprising a tower support 66 mounted on a motor vehicle (not shown). A vertical tower 67 is mounted on the tower support 66, and a telescoping boom 68 is mounted on the tower 67. Affixed to the tower 67 are a pair of clevis rings 69 and 70 having a pair of clevises 71 and 72 rotatably mounted thereon. The telescoping boom 68 is comprised of a tubular lower boom member 73 and a cylindrical boom extension member 74. A hook 75 is affixed to one end of the boom extension member 74, and tabs 76 and 77 are affixed to the lower boom member 73. A boom tang plate 78 affixed to one end of the lower boom member 73 is pivotally mounted on the clevis 72 by means of a clevis pin 80. A tab 87 is affixed to the lower portion 79 of the boom extension member 74 below the hook 75.

A grooved annular collar support 81 is affixed to the boom extension member 74 by means of welds 82. A collar 83 having a tab 84 is rotatably mounted on the collar support 81. Since the boom extension member 74 is of round cross section and is rotatably and slidably mounted in the lower boom member 73, the boom extension member 74 together with the hook 75 and tab 87 are free to rotate with respect to the remainder of the apparatus. v

A hydraulic cylinder assembly 85 is pivotally connected at one end to the lower boom member tab 77 and pivotally connected at the end of its extension rod 86 to the tab 84. Another hydraulic cylinder 89 is pivotally connected at one end to the tab 76 and at the other end to the clevis 71.

Operation of the apparatus shown in FIGS. 6 and 7 is generally similar to that shown in FIGS. 1-5. However, the apparatus of FIGS. 6 and 7 has an advantage when the apparatus is utilized on non-level terrain. For example, when the apparatus of FIGS. 1-vehicle at a pitched angle, the boom which has a rectangular cross section and the hydraulic cylinder utilized to extend the boom twist with respect to each other as a result of the cylinder 46 being extended at an inclined angle and being drawn vertically downward by the force of gravity. However, when the apparatus of FIGS. 6 and 7 is utilized, since the lower boom member 73 and boom extension member 74 are both round, and the boom extension member is free to rotate within the lower boom member, and moreover, since the boom extension member can rotate within the collar 83, both the hook 75 and the tab 87 are free to rotate with the boom extension member 74 and to permit the hydraulic cylinder 46 supported by the tab 87 to revolve until it hangs vertically downward, regardless of the pitch angle of the vehicle or the terrain.

Referring to FIG. 8, a portion of a modified form of the apparatus is illustrated, similar structures utilizing the same numbers as in FIGS. 6 and 7. A collar is affixed to the boom extension member 74 by welds 96 and has a tab 101 pivotally connected to the hydraulic cylinder extension rod 86. A grooved annular collar support 97 is aftlxed to the end of the boom extension member 74 by suitable means such as welding and has a collar 98 rotatably mounted thereon, and axially restrained thereby, and a tab 100 affixed to the collar. Affixed to the collar 98 by suitable means such as welding is a hook 99.

In operation, a cylinder 46 is pivotally mounted to the tab 100, and chains such as those designated as 53 in FIGS. 1-5 are mounted on the book 99. When the vehicle supporting the apparatus is pitched at an angle with respect to horizontal, the assembly including the boom assembly rotates to the same angle as the pitched vehicle. With a cylinder 46 mounted on the tab 100 and a chain 53 mounted on the hook 99, the hook and tab rotate to permit the cylinder 46 and chain 53 to remain in vertical position, thereby avoiding any tendency to twist the boom and its operating cylinder.

In the embodiment shown in FIG. 9 a grooved annular collar support 103 is affixed to the end of the boom by means such as welding and has a collar 104 rotatably mounted thereon with a hook 105 affixed to the collar. A universal joint 106 connects the lift cylinder 46 to the boom extension tang 42. A ball and socket joint 107 connects the cylinder 46 to the base plate 47. If desired, a ball and socket joint may be used in place of the universal joint 106.

In operation, when the vehicle is pitched at an angle and the boom assembly twists, the hook 105 rotates to the vertical position and the cylinder 46 revolves about the universal joint 106 until it hangs in a vertical position.

FIG. illustrates a further modified embodiment having a collar 110 with a tab 119 affixed to the boom 74 by welds 111. A cylindrical recess 112 is provided in the end of the boom 74, and has a grooved shaft 113 whose one end 114 is rotatably mounted in the recess 112 and whose other end 115 extends through an aperture in a cap 116 threadedly mounted over the end of the boom 74. The cap 116 cooperating with a split washer 121 provides axial restraint for the shaft 113. Fixedly mounted on the shaft end 115 are a collar 117 having a tab 120 and a hook 118.

The operation of the embodiment of FIG. 10 is similar to that of FIGS. 8 and 9. When the boom rotates as a result of the vehicle being positioned at a pitched angle, the shaft 113 rotates, permitting both the chain 53 affixed to the hook 118 and the cylinder 46 affixed to the tab 120 to revolve and to assume a vertical position.

Although it is not intended to so limit the scope of the invention, in a practical working embodiment the arrangement is such that the boom can rotate about a vertical axis through an arc of about 270. The boom is arranged to have a travel radius of 108 inches and to operate vertically through a 75 arc. Power for the hydraulic cylinders is supplied by a pump driven by the vehicle transmission through a power take-off. Each cylinder is individually activated by a double-acting control valve.

The post-pulling apparatus of the present invention has a number of advantages over prior art devices. First, it may be readily mounted on a vehicle. Second, it utilizes a post-pulling hydraulic cylinder adapted to have one end buttressed against the ground and to provide a strong pulling force independent of the weight or balance of the supporting vehicle. Third, the device has a telescoping boom which can swing horizontally, be extended radially, and raised or lowered, thereby permitting the post-pulling operation to be carried out at a considerable distance from the supporting vehicle. Additionally, the operating controls are conveniently mounted on the boom in a position well-suited to the convenience of the operator. Further, the apparatus is relatively inexpensive to construct from conventional components and materials and is readily operated by even unskilled workmen.

In addition, the apparatus of the present invention has the advantageous and desirable characteristic of providing such an apparatus which, although mounted on a vehicle, can be operated so as to apply little or no force against the vehicle itself.

It is to be understood that the invention is not to be limited to the exact details of operation or exact compounds, compositions, methods, or procedures shown 5 adapted to be mounted on a vehicle comprising a. a support adapted to be mounted on said vehicle,

b. a boom pivotally mounted at one end with respect to said support and adapted to revolve about a vertical axis and additionally to be raised and lowered, said boom comprising a pair of telescopingly arranged boom members,

0. first hydraulic cylinder means mounted with respect to said support and said boom and adapted for raising and lowering said boom angularly,

d. second hydraulic cylinder means affixed to said boom members and adapted to extend and retract said boom members with respect to each other,

e. third hydraulic cylinder means pivotally connected at one end to the remote end of said boom and having a ground-engaging support means mounted at the other end, and

f. means on the remote end of said boom for engaging means adapted to engage and grip a post to be pulled from the ground.

2. An apparatus according to claim 1, wherein said means for raising and lowering said boom comprises a tower vertically positioned and affixed at one end to said support, said boom being pivotally connected to the base of said tower and said first hydraulic cylinder means being pivotally connected at one end to an elevated portion of said tower and at the other end to said boom.

3. An apparatus according to claim 2, wherein valve means is provided for neutralizing said first hydraulic cylinder means when said post lifting hydraulic cylinder means is being operated, thereby permitting said boom to be raised and lowered by said third hydraulic cylinder means.

4. An apparatus according to claim 1, wherein said ground-engaging support comprises a base plate having ground-penetrating protuberances mounted thereon.

5. An apparatus according to claim 4, wherein the support mounted on said vehicle is provided with a support plate affixed thereto and provided with apertures to engage the protuberances of said base plate and to support said base plate during storage of said apparatus.

6. An apparatus'according to claim 1, wherein said boom members have a substantially rectangular crosssection.

7. An apparatus according to claim 1, wherein a hook is provided at the remote end of said boom to engage said means for engaging and gripping a post.

8. An apparatus according to claim 1, wherein said boom is provided with a control valve support and has a plurality of control valves mounted thereon.

9. An apparatus according to claim 2, wherein a pair of vertically spaced-apart clevis rings are mounted on said tower each having a clevis rotatably mounted thereon, one end of said boom being pivotally connected to the lower of said clevises and one end of said first hydraulic cylinder means being pivotally connected to the upper of said clevises.

10. An apparatus according to claim 1, wherein said means for engaging and gripping a post comprises a chain having its ends connected to a scissors-form clamp adapted to clamp a post.

11. An apparatus according to claim 1, including (g) means for engaging and gripping a post.

12. An apparatus according to claim I, wherein said third hydraulic cylinder means (e) is additionally connected to revolve about the axis of said boom.

13. An apparatus according to claim I wherein one of said boom members is rotatably mounted in the other, wherein a support for said third hydraulic cylinder (e) and a hook are affixed to the end of said rotatable boom member, and wherein collar means rotatably mounted and axially restrained on said rotatable boom member is connected to one end of said second hydraulic cylinder means.

14. An apparatus according to claim 1, wherein a collar is rotatably mounted on said boom having means pivotally connected to said third hydraulic cylinder 17. An apparatus according to claim 1, having a cylindrical recess provided in the end of said boom and a shaft rotatably mounted therein, a hook affi xed to the end of said shaft, and means affixed to said shaft pivotally connected to one end of said third hydraulic cylinder means (e) thereby permitting said third hydraulic cylinder means to revolve about the axis of said boom.

UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No. 3,848,850 8 Dated November 1 1 74.

Inventor) JOHN H. BEMIS It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Patent Reads: Assignment Reads:

"Bemis & Sons, Inc. -'--Bemis & Son, :Inc

Signed and sealed this 11th day of March 1975.

(SEAL) Attest:

' C. ITARSHALL DANN RUTH c MASON Commissioner of Patents Attestlng Officer and Trademarks UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent: No. 3,848,850 Date November 19. 1974 Inventor(s) John H. Benn s It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

PATENT READS: TA Pl LICATION READS:

Related Applicatien dat "Feb.- 2, 1973" --Jan. 2, l973-- Col. 4, line 27: Page 6b, line 5:

Figs. l vehicle" ---Figs. 1-5 is utilized with the vehicle-- Signed and sealed this 21st day of January 1975.

(SEAL) Attest:

MCCOY M. GIBSON JR. c. MARSHALL DANN Attesting Officer Commissioner of Patents OBM PO-105O (10-69) USCOMM-DC 60376-P69 i as. GOVERNMENT mumnc omcz; 1909 o-ass-a'u 

1. A hydraulically operated post-pulling apparatus adapted to be mounted on a vehicle comprising a. a support adapted to be mounted on said vehicle, b. a boom pivotally mounted at one end with respect to said support and adapted to revolve about a vertical axis and additionally to be raised and lowered, said boom comprising a pair of telescopingly arranged boom members, c. first hydraulic cylinder means mounted with respect to said support and said boom and adapted for raising and lowering said boom angularly, d. second hydraulic cylinder means affixed to said boom members and adapted to extend and retract said boom members with respect to each other, e. third hydraulic cylinder means pivotally connected at one end to the remote end of said boom and having a ground-engaging support means mounted at the other end, and f. means on the remote end of said boom for engaging means adapted to engage and grip a post to be pulled from the ground.
 2. An apparatus according to claim 1, wherein said means for raising and lowering said boom comprises a tower vertically positioned and affixed at one end to said support, said boom being pivotally connected to the base of said tower and said first hydraulic cylinder means being pivotally connected at one end to an elevated portion of said tower and at the other end to said boom.
 3. An apparatus according to claim 2, wherein valve means is provided for neutralizing said first hydraulic cylinder means when said post lifting hydraulic cylinder means is being operated, thereby permitting said boom to be raised and lowered by said third hydraulic cylinder means.
 4. An apparatus according to claim 1, wherein said ground-engaging support comprises a base plate having ground-penetrating protuberances mounted thereon.
 5. An apparatus according to claim 4, wheRein the support mounted on said vehicle is provided with a support plate affixed thereto and provided with apertures to engage the protuberances of said base plate and to support said base plate during storage of said apparatus.
 6. An apparatus according to claim 1, wherein said boom members have a substantially rectangular cross-section.
 7. An apparatus according to claim 1, wherein a hook is provided at the remote end of said boom to engage said means for engaging and gripping a post.
 8. An apparatus according to claim 1, wherein said boom is provided with a control valve support and has a plurality of control valves mounted thereon.
 9. An apparatus according to claim 2, wherein a pair of vertically spaced-apart clevis rings are mounted on said tower each having a clevis rotatably mounted thereon, one end of said boom being pivotally connected to the lower of said clevises and one end of said first hydraulic cylinder means being pivotally connected to the upper of said clevises.
 10. An apparatus according to claim 1, wherein said means for engaging and gripping a post comprises a chain having its ends connected to a scissors-form clamp adapted to clamp a post.
 11. An apparatus according to claim 1, including (g) means for engaging and gripping a post.
 12. An apparatus according to claim 1, wherein said third hydraulic cylinder means (e) is additionally connected to revolve about the axis of said boom.
 13. An apparatus according to claim 1 wherein one of said boom members is rotatably mounted in the other, wherein a support for said third hydraulic cylinder (e) and a hook are affixed to the end of said rotatable boom member, and wherein collar means rotatably mounted and axially restrained on said rotatable boom member is connected to one end of said second hydraulic cylinder means.
 14. An apparatus according to claim 1, wherein a collar is rotatably mounted on said boom having means pivotally connected to said third hydraulic cylinder means (e) at one end thereof, thereby permitting said cylinder to revolve about the axis of said boom.
 15. An apparatus according to claim 14, additionally having a hook affixed to said collar.
 16. An apparatus according to claim 1, having a universal coupling affixed at one end to said boom and having said third hydraulic cylinder means (e) pivotally connected to the other end of said universal coupling.
 17. An apparatus according to claim 1, having a cylindrical recess provided in the end of said boom and a shaft rotatably mounted therein, a hook affixed to the end of said shaft, and means affixed to said shaft pivotally connected to one end of said third hydraulic cylinder means (e) thereby permitting said third hydraulic cylinder means to revolve about the axis of said boom. 